1. Field of the Invention
The present invention generally relates to semiconductor processing technologies and, more particularly, to a system and process that removes a conductive layer from the edge and/or bevel of a workpiece and renders these areas free from unwanted impurities.
2. Description of the Related Art
In the semiconductor industry, various processes can be used to deposit and remove conductive materials on the wafers. Deposition techniques include processes such as electrochemical deposition (ECD) and electrochemical mechanical deposition (ECMD). In both processes, a conductor such as copper is deposited on a semiconductor wafer or a workpiece from an electrolyte that comes into contact with the surface of the wafer and another electrode. Material removal techniques include chemical etching (CE), electrochemical etching (ECE), electrochemical mechanical etching (ECME) and chemical mechanical polishing (CMP), which are used to remove the unwanted excess portions of materials from the workpiece surface.
The term of Electrochemical Mechanical Processing (ECMPR) is used to include both Electrochemical Mechanical Deposition (ECMD) processes as well as Electrochemical Mechanical Etching (ECME), which is also called Electrochemical Mechanical Polishing (ECMP). It should be noted that in general both ECMD and ECME processes are referred to as electrochemical mechanical processing (ECMPR) since both involve electrochemical processes and mechanical action on the workpiece surface.
In one aspect of an ECMPR method, a workpiece-surface-influencing-device (WSID) such as a mask, pad or a sweeper is used during at least a portion of the electrotreatment process when there is physical contact or close proximity and relative motion between the workpiece surface and the WSID. Descriptions of various deposition and etching methods, including planar deposition and planar etching methods i.e. ECMPR approaches and apparatus, can be found in U.S. Pat. No. 6,176,952 entitled xe2x80x9cMethod and Apparatus For Electro Chemical Mechanical Depositionxe2x80x9d, and U.S. application Ser. No. 09/740,701 entitled xe2x80x9cPlating Method and Apparatus that Creates a Differential Between Additive Disposed on a Top Surface and a Cavity Surface of a Workpiece Using an External Influence,xe2x80x9d filed on Dec. 18, 2001, both commonly owned by the assignee of the present invention.
Other material deposition and removal methods are understood and need not be further described.
Regardless of the deposition or removal process used, conventionally the workpiece is transferred to some type of cleaning and drying station after processing. During the cleaning steps, various residues generated by the processing are rinsed off the workpiece, and subsequently the workpiece is dried by spinning and if necessary blowing nitrogen on its surface.
In one design, the processing chamber, in which conventional plating or removal processing or ECMPR occurs, and the rinse chamber can be stacked vertically in a vertical process chambers arrangement. In this arrangement, the processing can be performed in a lower chamber, and the cleaning and drying can be carried out in an upper chamber after isolating the upper chamber from the lower chamber so that chemicals used in either chamber do not mix with each other. One such vertical chamber is disclosed in the co-pending U.S. application Ser. No. 09/466,014, now U.S. Pat. No. 6,352,623 entitled xe2x80x9cVertically Configured Chamber Used for Multiple Processesxe2x80x9d, filed Dec. 17, 1999, commonly owned by the assignee of the present invention.
Conventionally, a typical processing sequence is to initially perform deposition or plating of a conductive material onto a workpiece, and thereafter remove some of the previously deposited conductive material, such as the unwanted overburden conductive material from the front face of the workpiece.
Copper is a preferred conductive material used for integrated circuit (IC) interconnects and packaging applications. ECD and ECMD processes can deposit copper. Therefore it will be used as an example.
When copper is plated on a wafer front surface, in addition to areas where there are ICs, it may also deposit on the edges and sides, i.e., bevel, of the wafer where no ICs or circuits are located. In some cases, the edge and bevel are protected from the plating solution; therefore no copper may be plated there. However, there may still be a copper seed layer on the edge regions and bevel. Whatever the source is, such remaining copper, i.e. the edge copper, may migrate to neighboring active regions from the sides and edges of the wafer, especially during an annealing step. Further, copper particles originating from a wafer edge may contaminate the wafer transport system, and other process equipment such as the annealing system etc., and so be passed on to contaminate other wafers. Poorly adhering copper flakes from the wafer edge may also cause problem during the CMP step by becoming loose and getting onto the surface areas where there are circuits. For these reasons and more, it is important to remove the copper from the edges and the bevel of the wafer following each copper plating process step.
U.S. Pat. No. 6,309,981 describes a method of removing metal from the edge bevel region of a semiconductor wafer. U.S. Provisional Application No. 60/276,103, an application assigned to the assignee of the present invention, describes a method and apparatus for removing edge copper in an upper rinsing chamber of a vertical chamber system that also includes a lower processing chamber.
In both of the above documents, the chemical removal approaches use aggressive etching solutions with oxidizers, such as sulfuric acid and hydrogen peroxide mixtures or strongly oxidizing acids such as nitric acid. Such aggressive etching solutions are designed so that the oxidizers chemically oxidize the copper and the oxidized copper dissolves in the acidic solution. To be able to obtain high process throughput the aggressive etching solutions are formulated to yield very high etching rates such as larger than 300-400 A/sec, preferably larger than 1000 A/sec, for copper. This corresponds to an etching rate of much higher than 20000 A/min. Although aggressive etching solutions and systems employing them are presently in use there are some issues associated with their utilization.
Strong oxidizers such as hydrogen peroxide are not very stable; therefore, mixing, transport and storage of the aggressive edge copper removal etchants present a challenge. For example, solutions containing hydrogen peroxide need to be shipped in breathable containers that do not allow pressure built-up in the container due to hydrogen peroxide break-up. These etching solutions also have a limited lifetime due to breakdown of the oxidizer. It is also challenging to attempt removal of material from the front face edge of the workpiece and maintain separation of the aggressive etching solution from front face portions other than the edge of the workpiece. As stated earlier, aggressive etching solutions are designed to etch copper at very high rates. Therefore any droplets inadvertently ending up on other portions of the wafer surface would etch these areas and cause oxidation and potential failure in IC""s. Even the vapor of aggressive etching solutions causes oxidation and discoloration of the portions of the copper surface, especially adjacent to the edge where material removal is performed. Such oxidized regions need to be typically cleaned after the edge copper removal process, using a different acid solution with very low chemical etching rate. This makes it necessary to store and deliver yet another solution chemistry to the wafer surface and therefore adds to the cost. There is another consideration in using aggressive etching solutions specifically for vertical chamber structures such as shown in FIG. 5. In these systems the upper chamber and lower chamber are well isolated by flaps or other means of barriers. However, if there is any accidental leak and drops of the edge copper removal solution finds its way to the lower chamber, it can mix with the electroprocessing solution and cause problems.
U.S. Pat. No. 6,056,869 describes a device for deplating metal from side edges and a backside of a semiconductor wafer for chemical mechanical polishing that uses a specific electrochemical etching approach using a specific device design. In this patent, an etching solution is delivered to the whole backside of the wafer and it is used to electrochemically deplate metal from the edges and the back side while the upper side of the wafer is protected from the etchant by an inert fluid jacket.
Thus, there is a need in the semiconductor industry for systems and processes that allow for more efficient processing, including the removal of edge copper from a front face of the wafer, and removal of edge copper as part of other cleaning processes.
It is an object of the present invention to provide a method and apparatus for removing edge conductor that exists on a workpiece.
It is a further object of the present invention to provide a method and apparatus for removing an edge conductor using a directed stream of a mild etching solution applied to the edge of a workpiece.
It is a further object of the present invention to increase etching ability of a very low-etch-rate solution by passing a current through that solution and selectively delivering that solution upon an edge conductor of a wafer.
It is a further object of the present invention to provide a system that allows the same mild etching solution to remove an edge conductor and also clean the front surface of the workpiece.
It is a further object of the present invention to provide a system that allows the same mild etching solution to deposit the conductor on the front surface of the workpiece and also remove an edge conductor.
It is still a further object of the present invention to provide a system that allows for edge conductor removal, workpiece front surface cleaning, or both to be performed in the same processing chamber that is used for deposition or removal processing of the workpiece.
The above objects of the invention, among others, either singly or in combination, are achieved by the present invention by providing an edge cleaning system and method in which a directed stream of a mild etching solution is supplied to an edge area of a rotating workpiece, including the front surface edge and bevel, while a potential difference between the workpiece and the directed stream is maintained.
In one aspect, the present invention provides an edge cleaning system that is disposed in the same processing chamber that is used for deposition or removal processing of the workpiece.
In another aspect, the mild etching solution used for edge removal is also used to clean the front surface of the wafer, either simultaneously with or sequentially with the edge removal process.